1. Field of the Invention
This invention relates to machines and apparatus for polishing semiconductor wafers, and more particularly to a machine for the chemical mechanical planarization (CMP) polishing of semiconductor wafers and the detection of planarization end point.
2. Description of Related Art
The machines to prepare and fabricate semiconductor wafers are well known in the art. Semiconductor wafers are prepared by slicing thin sheets from a semiconductor crystal. The thin sheets are then abraded and polished to eliminate any surface irregularities and to achieve a planar surface.
Integrated circuits (IC's) are then imprinted upon the surface of the semiconductor wafer. The IC's are formed by selective deposition and removal of layers of semiconducting materials, conducting metals such as Aluminum or Tungsten, and insulating materials such as Silicon Dioxide.
The planarization of the semiconductor wafer and the removal of the aforementioned layers may require abrading and polishing. The polishing process may be accomplished by an abrasive slurry lapping process. In this process a semiconductor wafer is mounted on a rotating carrier and placed in contact with a rotating polishing pad. The abrasive slurry is sprayed upon the rotating polishing pad. The material is removed from the semiconductor wafer by the mechanical abrading action of the slurry.
The slurry is a liquid having insoluble abrasive particles held in suspension. Additionally the liquid may have chemical abrasion properties. This form of polishing is referred to as chemical mechanical planarization (CMP).
A particular problem encountered in the use of CMP polishing is in the control of the process parameters to achieve a particular smoothness or to a particular thickness of the deposited materials. In the past, the surface characteristics and the planarization end point of the planarization of the wafer have required the removal of the semiconductor wafers from the polishing apparatus and physically examining the semiconductor wafers to determine dimensional and planar characteristics. The semiconductor wafers must be repeatedly loaded into and removed from the polishing apparatus to complete the planarization process. Additionally excess materials may be removed from the semiconductor wafer, thus causing the semiconductor wafer to be discarded.
U.S. Pat. No. 5,196,353 (Sandhu, et al.) describes a method and apparatus for an in situ determination of planarization end point using thermal imaging during CMP polishing.
U.S. Pat. No. 5,308,438 (Cote, et al.) discloses another method and apparatus for determining a planarization end point in the CMP polishing of layers on a semiconductor workpiece using CMP polishing. The apparatus detects changes in the load current of a motor rotating said semiconductor workpiece.
U.S. Pat. No. 5,337,015 (Lustig, et al.) shows still another method and apparatus for in situ thickness monitoring and planarization end point detection. In this case an electrical signal is passed through the semiconductor wafer and changes in the signal are monitored to detect changes at the surface being polished.
U.S. Pat. No. 5,240,552 (Yu, et al.) discloses yet another apparatus for the detection of planarization end point during CMP polishing of a semiconductor wafer using acoustical waves. The acoustical waves are transmitted through the wafer and the reflected acoustic waves are analyzed to determine the planarization end point and the semiconductor wafer thickness.
U.S. Pat. No. 5,483,568 (Yano,et al.) illustrates a method for determining CMP polishing rate on the surface of a semiconductor wafer. An x-ray beam is directed to an exposed surface of a polishing pad during the CMP polishing of the semiconductor wafer. The intensity of the x-ray fluorescence, which results from the x-ray beam illuminating the polishing pad is detected. The intensity of the fluorescence is related directly to the CMP polishing rate.